1. Field of the Invention
The present invention relates to the preparation of trichlorosilane-based admixture well adapted for the production of semiconductor grade elemental silicon therefrom.
2. Description of the Prior Art
It is known to this art to prepare high grade silicon by decomposing chlorosilanes, preferably trichlorosilane.
Trichlorosilane, upon decomposition thereof, leads to the formation of significant amounts of silicon tetrachloride, such decomposition of trichlorosilane taking place according to the reaction: EQU 4HSiCl.sub.3 43 Si+3SiCl.sub.4 +2H.sub.2
Furthermore, the synthesis of silane, SiH.sub.4, by dismutation of trichlorosilane also gives rise to the formation of silicon tetrachloride which must then be converted back into the starting material trichlorosilane.
It too is known to convert such silicon tetrachloride into trichlorosilane by thermal reduction thereof, with hydrogen, according to the reaction: EQU SiCl.sub.4 +H.sub.2 .revreaction.SiCl.sub.3 +HCl
Since this reaction is balanced, the production of trichlorosilane is facilitated by increasing the temperature and tempering the reaction medium, e.g., by sudden cooling, in order to militate against the reverse reaction. Hence, it too has been proposed, for example in British Patent No. 924,545, to conduct the thermal reduction of silicon tetrachloride with hydrogen in a plasma and by projecting the reaction mixture against an appropriately chilled metal surface to thereby attain a proper tempering of said reaction mixture.